Monoclonal antibodies (MAbs) have been generated and characterized using membrane enriched fractions of human carcinoma metastases. These antibodies have been characterized as to reactive antigen, and the presentation of antigen on human mammary and colon carcinoma cell populations and normal human tissues. MAb B72.3 has been shown to be reactive with a 220,000 to 400,000d glycoprotein complex expressed in approximately 50% of human mammary tumors, greater than 85% of human colon carcinomas, but is not expressed to any significant extent in any adult human tissues thus far tested. MAb B72.3 is currently being evaluated for its use in the detection of occult adenocarcinoma cells in pleural effusions, and for the in situ radioimmunodetection of metastases in carcinoma patients. Antigenic phenotyping with MAb B72.3 revealed that little correlation exists between the expression of the B72.3 reactive antigen in primary tumor cells of a colon carcinoma mass and its expression in tumor cells of regional node or distal metastases. A correlation was shown to exist, however, between the expression of this antigen in tumor cells of regional nodes and those in distal metastases. These findings suggest that the effective use of monoclonal antibodies for diagnostic imaging of distal metastases may require the evaluation of the antigenic expression on tumor cells in regional lymph nodes rather than the primary lesion. Monoclonal antibodies have recently been generated to human laminin receptor and the p21 human ras gene product. These are currently being evaluated to determine if any correlations exist between the expression of the laminin receptor and/or ras p21 in specific cell populations and the processes of carcinoma initiation, promotion, or progression.